As flash memory technology becomes more advanced, flash memory is replacing traditional magnetic hard disks as storage media for mobile systems. Flash memory has significant advantages over magnetic hard disks such as having high-G resistance and low power dissipation. Because of the smaller physical sizes of flash memory, they are also more conducive to mobile systems. Accordingly, the flash memory trend has been growing because of its compatibility with mobile systems and low-power feature.
New generation personal computer (PC) card technologies have been developed that combine flash memory with architecture that is compatible with the Universal Serial Bus (USB) standard. This has further fueled the flash memory trend because the USB standard is easy to implement and is popular with PC users. In addition to replacing hard drives, flash memory is also replacing floppy disks because flash memory provides higher storage capacity and faster access speeds than floppy drives.
However, the USB standard has several features that require additional processing resources. These features include fixed-frame times, transaction packets, and enumeration processes. For better optimization, these features have been implemented in application-specific integrated circuits (ASICs).
A problem with a USB mass-storage devices is that they are slow. The USB interface is significantly slower than IDE interface in particular. This is because of the overhead associated with the USB standard, which include additional resources required for managing USB commands and handshake packets. Bulk-only transactions introduced by the USB standard have relieved some resources but only if the USB traffic is not too busy.
In addition to the limitations introduced by the USB standard, there are inherent limitations with flash memory. First, flash memory sectors that have already been programmed must be erased before being reprogrammed. Also, flash memory sectors have a limited life span; i.e., they can be erased only a limited number of times before failure. Accordingly, flash memory access is slow due to the erase-before-write nature and ongoing erasing will damage the flash memory sectors over time.
To address the speed problems with USB-standard flash memory, hardware and firmware utilize existing small computer systems interface (SCSI) protocols so that flash memory can function as mass-storage devices similarly to magnetic hard disks. SCSI protocols have been used in USB-standard mass-storage devices long before flash memory devices have been widely adopted as storage media. Accordingly, the USB standard has incorporated traditional SCSI protocols to manage flash memory.
A problem with SCSI protocols is that they do not include an erase command to address the erase-before-write nature of flash memory. Accordingly, the erase operation is handled by the host system, which further ties up the host system resources.
Some solutions have been introduced that involve new USB packet definitions such as write flash, read flash, and erase flash definitions. However, these definitions are not an efficient way to handle flash memory because they introduce additional protocols that require additional computing resources at the host system. They also do not address the sector-wear issues.
Another solution provides a driver procedure for flash memory write transactions. This procedure has three different sub-procedures. Generally, the data of a requested flash memory address is first read. If there is data already written to that address, the firmware executes an erase command. Then, if the erase command executes correctly, the firmware executes a write request. However, this driver procedure utilizes protocols that require additional computing resources at the host system.
Another solution provides a flash sector format that has two fields: a data field and a spare field. The spare field contains control data that include flags that facilitate in the management of the sectors. However the flags introduce ASIC complexity when the host system writes to the sectors.
Disadvantages of many of the above-described and other known arrangements include additional host system resources required to process special protocols and the resulting added processing time required for managing flash memory.
Accordingly, what is needed is an improved system and method for controlling flash memory. The system and method should be able to comply with the USB standard, should be suitable for ASIC hardware implementation, and should be simple, cost effective and capable of being easily adapted to existing technology. The present invention addresses such a need.